Twelve-point nut



July 14, 1964 w, GRlMM 3,140,636

TWELVE-POINT NUT Original Filed Nov. 14, 1957 l2 Q-JO 14 wav FIG. Z

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INVENTOR. DA l/ID W. GR/MM A TTORNE Y United States Patent 3,140,636TWELVE-POINT NUT David W. Grimm, Fullerton, Califi, assignor, by mesneassignments, to Kaynar Mfg. Co., Inc., Pica-Rivera, Calif., acorporation of California Continuation of application Ser. No. 696,503,Nov. 14, 1957. This application Sept. 20, 1962, Ser. No. 226,478 3Claims. (Cl. 85-32) This invention relates to threaded fasteners andmore specifically to lock-nuts adapted for use in applying high tensilestresses to their mating bolts and which are of minimum weight and bulkso as to be especially adapted for use in applications requiring highresistance to stress and to loosening from vibration in aircraftconstructions.

This application is a continuation of my application, Serial No.696,503, filed November 14, 1957, now abandoned, for Twelve-Point Nut.

In the present state of development of the art, aircraft lock-nuts fornormal purposes, based upon relatively thin and lightweightconstructions, have come into extensive general use. However, forextraordinarily high tensile applications a relatively greaterresistance to thread stripping due to axial forces and failure due tohoop tension is necessary, and so-called high-tensile nuts have beendeveloped.

High-tensile nuts have been characterized by the provision of greaterheight to provide greater thread engagement area or by the provision ofthicker or reinforced wall constructions, or both, and such factors tendto increase weight. In the effort to keep weight increase to a minimumthe industry has resorted to increasing the number of sides of the outerperimeter of the nut beyond the conventional six sides (hexagon). Thisresults in relatively thickening the least wall thickness of a givensize nut. In view of the availability of socket type wrenches havingtwelve wrenching points, the so-called twelve-point nut (as discussed inU.S. Patent 2,588,372, issued to George H. Erb on March 11, 1952) hasevolved and such constructions provide a relatively thicker minimum wallin a comparatively small perimetral form so that it is possible (asstated in the patent) to utilize stand ard socket Wrenches one size lessthan usual for a given thread size. Moreover, such constructions havethe im portant incidental advantage that more wrenching surfaces areprovided, resulting in a greater number and area of wrench contacts tobetter enable high torques to be applied without injury either to thesurface of the nuts or of the wrenching tools used thereon.

The disclosure of the Erb patent indicates that it was essential, intwelve-point lock-nuts, that the wall thickness be the maximum thatwould permit a wrench to engage the outer surface since the wallstrength required was critical for the undersized outer perimeterinvolved, said outer surface being described by Erb as a double hexagonformed by two hexagons offset circumferentially and providing anexternal configuration having an inscribed circle of a greater diameterthan that of a single hexagon having the same distance across the flats,and this wall thickness was considered critical since it is included asa limitation in the claims of the patent. As described, thisconfiguration, in a less than standard outer size, resulted in a weightsaving over conventional-sized square and hexagonal nuts. However, theconfiguration is of maximum weight and bulk for a twelve-pointperimetral form.

In the prior art, as represented by Erb, it was common to provideseparate load carrying and locking portions of a nut. Thus, in the Erbconstruction, the locking feature, involving an additional axial lengthof the lock-nut, does not contribute to the axial stressing of the bolt.Accordingly, the stresses or load of the nut were entirely 3,140,636Patented July 14, 1964 ice in the load-carrying portion and the walls ofthe loadcarrying portion had to be at least as thick as claimed by Erbto obviate structural failure.

The Erb construction is typical of the known prior art in the separationof the loading and locking functions. Another example of the prior artis the so-called beam type which is an all metal construction whereinthe locking end of the nut is formed with longitudinal slits and theresulting threaded strips or beams are bent slightly inwardly to cause aresilient gripping of a bolt threaded therethrough. In this lastdescribed form the slit portions provide no substantial resistance tohoop stresses, of course, and as a result the main body of the nut mustbe beefed up as much as possible, as in the Erb construction.

The present invention provides a construction wherein the weight ofhigh-tensile nuts of the class described may be substantially reducedwhile providing improved resistance to failure of the nuts, andretaining the advantage of added wrenching surfaces of twelve-pointconfigurations. This is accomplished by providing a locking featurewhich is capable of performing a load-carrying function as well as alocking function so that the load is distributed over the full length ofthe nut rather than only partially as in the prior art. As a result themain body of the nut is subject to less stress per unit height and fornuts of substantially the same height as prior art nuts, the wallthickness of the main body may be safely reduced to less than thecritical minimum taught by Erb, with a substantial savings in weight.

As a related advantage of the present invention it is possible to formthe nut body, the threads and the lock ing portion by working on thepiece in a relatively soft state and subsequently hardening it to agreater degree than possible in the prior art whereby strongerstructures are possible in a unitary construction, as distinguished fromprior art multiple piece lock-nuts or prior art structures wherein thelocking features are such as to place practical limitations on thehardness of the finished nut. Thus, the plastic insert of one type oflock-nut as embodied in Erb, cannot be subjected to heat treatment andthe nut body, therefore, cannot be hardened after the operationsinvolved in positioning the insert, and must be soft enough to permitforming operations incident to positioning the insert. Relative to thebeam type of lock- 7 ing feature described hereinabove, excessivehardening causes brittleness and unduly high and irregular torquecharacteristics of the locking beams and such devices are notpractically operable at unconventional hardnesses.

In the present invention the locking portion of the nut incorporatesload-bearing threads which are a continuation of those of the main bodyof the nut, and the locking portion is of relatively thin constructionand is imperforate and unbroken either radially or longitudinally. Theoverall construction may be hardened to ranges in excess of 36 on theRockwell C scale in contradistinction to the old standard 28-32 RockwellC as discussed in the Erb patent. The result of this greater hardness isa better over-all resilience for locking and for adaptation to threadtolerance variations and a greater strength per unit weight to give anovel construction of less weight and bulk and better operability thanwas possible in the prior art.

It is, therefore, an object of the present invention to providehigh-tensile type lock-nuts of improved operating characteristics and ofless weight and bulk than hitherto known.

A further object of this invention is to provide a twelve-pointhigh-tensile type lock-nut wherein the wall thickness may be less thanthe minimum previously regarded as critical for such devices by personsskilled in this art.

Another object of this invention is to provide a hightensile typelock-nut comprised of a single piece of metal formed and threaded inrelatively soft condition and subsequently hardened to unconventionalhardnesses.

Yet another object of the present invention is to provide novelhigh-tensile type lock-nut constructions wherein the locking portion ofthe nut serves as an unbroken continuation of the threads of the mainbody portion of the nut whereby to assist in performance of theloadbearing function of the nut.

Still another object of the invention is to provide a twelve-pointlock-nut construction wherein the thinnest wall thickness issubstantially the same as would exist for a simple hexagonal perimeter,thus providing the additional wrenching advantages of a twelve-pointconfiguration with a minimum addition of weight to the structure.

Other objects and many of the attendant advantages of this inventionwill be readily appreciated as the same becomes better understood byreference to the following detailed description when considered inconnection with the accompanying drawing in which like referencenumerals designate like parts throughout the figures thereof andwherein:

FIGURE 1 is a plan view of a preferred embodiment of a high-tensile nutaccording to this invention;

FIGURE 2 is a side elevation of the nut of FIGURE 1, with a portionthereof shown in section, and

FIGURE 3 is a greatly enlarged schematic showing of comparativecross-sections of high-tensile nuts of the twelve-point typeillustrating wall thicknesses of simple hexagon and double hexagonsections as compared with the wall thickness of the present invention.

Referring now to the drawing, FIGURES 1 and 2 comprise an exemplaryshowing of a twelve-point high tensile type lock-nut according to thepresent invention. The nut is an internally threaded unitary piece ofsuitable material for the resilience and strength requirements desired.A wide variety of materials may be utilized, it being requisite onlythat they be selected in their optimum state of formability ormachinability, provided such materials are of a type which can bestrengthened and hardened to a desired degree by a subsequent processsuch as heat treatment. Examples of materials capable of having suitablequalities before and after treatment are carbon steels, beryllium-copperalloys, and some stainless steels. Of course, other relatively soft,ductile materials capable of being hardened and strengthened to adesired degree by subsequent treatment may also be used.

The nut of the present invention is an internally threaded unitary piececomprising an enlarged base member which tapers upwardly and inwardly toa shank portion 11 which comprises a wreching portion 12, which isintegral with the base at one end and an integral thin-walled lockingportion 14 at its other end. The screw threads within the piece areindicated by the reference numeral 17, and are continuous from end toend of the nut.

The enlarged base portion 10 provides a flat enlarged bottom for hearingon the surface of the piece to which a connection is being made whentightened upon a bolt, and the additional material provided also servesto strengthen the nut at the point where it is most greatly loaded understress. It is noteworthy that the base construction is integral with theshank portion 11 rather than a separate piece and this simplification ofconstruction is made possible by the unconventional hardness of themetal of the entire nut which is elsewhere discussed, and obviates thenecessity of employing a separate base ring of material harder than theremainder of the nut for base reinforcement.

Base 10 tapers upwardly and inwardly to the main body or wrenchingportion 12 which is twelve-point external configuration and size forengagement by the equivalent points of standard socket wrench means of asize less than that which would normally be standard for the 4- size andtype of thread in the shank 11. The end of the wrenching portion 12remote from the base flares inwardly to the thin-walled locking portion14 of the nut.

Locking portion 14 is deformed at its extreme edge, after threading, toan elliptical configuration, and this deformation is generally gradual,causing gradual variation from perfectly round threads on the inner wallof the locking portion in the area of its juncture with the thickerwrenching portion to the most out-of-round thread at the extreme tip ofthe nut. By virtue of the thinness and resilience of the wall of thelocking portion a bolt inserted through the nut gradually deforms thelocking portion to a round form but the resilience of the walls exertgripping locking pressure on the bolt in their effort to return to theelliptical form. The continuous nature of the thread is such that someof the axial and hoop stresses are carried by the thread in the lockingportion.

As pointed out in the introductory remarks of this specification, priorart development of nuts of the class under discussion, for aircraftusage, resulted in other sizes which were of less than standard size forthe size thread involved in order to save weight but which had wallswhich were reinforced by a base ring and by the thickening resultingfrom using a double hexagonal perimetral form rather than the standardhex, to provide the necessary strength as well as the importantincidental advantage of increasing the available wrenching surfaces. Aspreviously pointed out, the wall thickness provided by the doublehexagonal form was considered a critical minimum in the prior art. Thegist of the present invention resides in my discovery that substantialweight savings may be made by further reduction of the minimum thicknessof the wall (as by cutting the inner points of the outer configurationmore deeply into the wall), while retaining the advantage of providingadditional wrenching surfaces, by the provision of integral unitarylocking means, such as the locking portion 14 of the present invention.As an added factor I have discovered that the use of such a lockingfeature allows hardening of the finished nut to Rockwell hardnesses inexcess of 36 on the C scale and preferably in the range of 40 to 50 onthe C scale, rather than to the 28 to 32 Rockwell C range previouslyimposed as a limitation on such lock-nuts by virtue of the nature oftheir constructions, and this added hardness results in strengtheningthe materials so that greater weight savings are possible without dangerof failure of the nut construction.

In view of the above, the cross-sectional configuration of the wrenchingportion of my novel nut construction may be in the form of atwelve-pointed figure wherein the inner points are defined by lineswhich are at substantially lesser angles than the 150 angle required asa critical parameter by the prior art. By virtue of the mechanicaladvantages attained by the imperforate integral locking device utilizedin my novel nut construction and by virtue of the higher hardnesses madepossible thereby I have found that the inner points may be more deeplysituated to an extent wherein the surfaces defining the inner points areat angles of less than the previously critical 150 with one another.Thus, in its broadest form, my invention involves reduction of the wallthickness by reducing the included angle between the contiguous surfaceswhich define the inner points of an angle less than the 150 consideredcritical by the prior art. It may be determined geometrically that at anangle of 138 the wall thickness would be the same as for a hexagonalouter shape. However, in practice, in order to fully take advantage ofthe weight savings which are safely made possible by the presentinvention, it is preferable to reduce the angle substantially, to arange between and and, as a matter of fact, the nuts are manufacturedwith angles of 133 between the surfaces defining the inwardly directedpoints. This construction, of course, requires less material and hasresulted in Weight savings of about 25% as compared with equivalentprior art nuts, and such savings are extremely critical in aircraftusages.

Attention is directed to FIGURE 3 for a graphic comparison of the wallthickness standards involved in the prior art criteria and in thepresent construction. The fragmentary schematic showing includes an are40 representative of the inner wall of the nut. This are may be assumedto be the position at a constant diameter of any selected referencepoint on the wall, such for example as the root or the crest of theinternal thread in the nut of a size and type to receive a bolt of astandard size. A single hexagonal outer perimeter is simulated by thedash line b and the arc of a circle inscribed therein by b, the distanceb" between the arc b and the are 40 representing the minimum wallthickness across the flats of the standard hexagonal perimetrical form.The dotted are a is representative of an arc of a circle inscribedWithin a double hexagonal form a, the distance a" representing theminimum wall thickness of the doublehex perimeter and graphicallyillustrating the greater thickness (and Weight) evolved by devices suchas that disclosed in the Erb patent discussed hereinabove. On the rightside of the figure, the lines c are representative of the wall surfacesdefining the inner points of the twelvepoint configuration of thepresent invention, as described hereinabove and as shown in FIGURES 1and 2, the hatched portion 42 representing material savings as comparedwith the double hexagonal form of Erb, for a preferred angularity of thewall surfaces of 133. The are c is representative of an arc of a circleinscribed within a twelve-point configuration such as represented by cc(and by FIGURES 1 and 2) with the stated 133 angle between the walls,and the distance c" represents the minimum wall thickness for thisconfiguration and is not only less for any given diameter of are 40 thanthat indicated as a critical minimum by Erb (the distance a) but alsoless than that provided by an undersized hexagonal form (the distanceb). This is especially true if the nut is threaded to receive a boltthat is a normal standard size for the overall or diagonal dimension ofa given nut having twelve points. Obviously, from the foregoing it maybe seen that the advantage of additional wrenching surfaces has beenpreserved, while maintaining the strength of the nut and substantiallyreducing its weight, this result being attained by the novel combinationof a unitary imperforate locking feature integral with the wrenchingportion of the nut. The added features of unitary reinforcing baseconstruction and high hardness are related adjuncts contributing to theimproved results.

Nuts according to this invention are made of material such as 4340 alloysteel (for example) in a state soft enough to permit relatively easyworking. The material is formed into a nut blank having a through boreand having the outer configuration herein described, either by amachining or forging operation. The blank is then threaded with acontinuous thread and the locking end portion of the blank is thendeformed to an elliptical shape which it holds because of the relativelysoft state of the material. The finished blank is then subjected totreatment, such as heat treatment, to raise its hardness above 36Rockwell C and preferably to a range between 40 and 50 Rockwell C.

From the above it may be seen that I have disclosed high-tensile typelightweight lock-nut constructions particularly adapted for aircraftusages and which provide improved strength, weight and lockingcharacteristics, by virtue of the novel combination of the variouselements thereof.

While the invention has been described in detail with reference to onespecific example, said example is intended to be illustrative ratherthan as limiting since various changes in structure and procedure areobviously within the scope of the present disclosure. Accordingly,

it is to be understood that the present invention is not to be limitedto the specific illustrative disclosure but rather by the scope andlanguage of the appended claims.

I claim:

1. A high tensile strength lightweight lock-nut comprising: aninternally threaded annulus having a main body portion with an outerwall configuration in the form of a regular polygon having twelveoutwardly extending points of a size to be engaged by standard sizewrench means of a size less than usual for the size thread involved, thecontiguous wall surfaces between two successive outwardly extendingpoints being at least in part substantially flat and lying in planesintersecting at an angle of about degrees to 138 degrees, the wall ofthe nut at the intersection of such contiguous wall surfaces having apositive but minimum radial dimension throughout the axial extent of theintersection of the wall surfaces, as measured to the base of saidthreads, not greater than the radial distance between the base of saidthreads and a concentric circumscribing circle equal in radius to acircle inscribed in a regular hexagon having the same major diagonaldimension across points as the said regular polygon with twelve points.

2. A high tensile strength lightweight lock-nut comprising: aninternally threaded annulus having a main body portion with an outerwall configuration in the form of a regular polygon having twelveoutwardly extending points and of a size to be engaged by standard sizewrench means of a size less than usual for the size thread involved, thecontiguous wall surfaces between two adjacent outwardly extending pointsbeing at an angle of 130 to 138 degrees to one another, the intersectionof such contiguous wall surfaces having a positive but minimum radialdimension throughout the axial extent of the intersection of the wallsurfaces, as measured to the base of said threads, not greater than theradial distance between the base of said threads and a concentric circleequal in radius to a circle inscribed within a regular hexagon havingthe same major diagonal dimension as the said polygon with twelvepoints, said main body portion tapering into an internally threadedintegral portion at one end thereof, said locking portion beingrelatively thinner than said main body portion, the locking portion andthe thread within the locking portion being noncircular at the endthereof remote from the main body portion, said nut having a hardnessabove 36 Rockwell C, whereby said locking portion exerts resilientlocking force on a bolt threaded therethrough while simultaneouslycarrying a portion of the axial and hoop stresses of the nut to assistthe main body portion of the nut in resisting said stresses, and wherebythe weight of the nut may be reduced without strength reduction whileproviding resilience in the area of the main body portion for betterconformation with the threads of matching bolts.

3. A high tensile strength lightweight lock-nut comprising: aninternally threaded annulus having a main body portion, said main bodyportion having an enlarged integral base at one end thereof to provide abearing surface and to reinforce the main body portion in the area ofgreater stress, said main body portion having an outer wallconfiguration in the form of a regular polygon having twelve outwardlyextending points and of a size to be engaged by standard size wrenchmeans of a size smaller than usual for the size thread involved, thecontiguous wall surfaces between two adjacent outwardly extending pointsbeing at an angle of 130 to 138 degrees to one another, the intersectionof such contiguous wall surfaces having a positive but minimum radialdimension throughout the axial extent of the intersection of the wallsurfaces, as measured to the base of said threads, not greater than theradial distance between the base of said threads and a concentric circleequal in radius to a circle inscribed within a regular hexagon havingthe same major diagonal dimension as the said polygon, the other end ofsaid main body portion tapering into an internally threaded integralcircumferentially continuous resilient locking portion at one endthereof, said locking portion being relatively thinner than said mainbody portion, the locking portion and the thread within the lockingportion being non-circular at the end thereof remote from the main 5body portion, whereby said locking portion exerts resilient lockingforce on a bolt threaded therethrough While simultaneously carrying aportion of the axial and hoop stresses of the nut to assist the mainbody portion of the nut in resisting said stresses, said nut having ahardness above 36 Rockwell C.

References Cited in the file of this patent UNITED STATES PATENTS GreenAug. 2, 1938 Green May 4, 1948 Erb Mar. 11, 1952 Reiner Dec. 17, 1957

1. A HIGH TENSILE STRENGTH LIGHTWEIGHT LOCK-NUT COMPRISING: AN INTERNALLY THREADED ANNULUS HAVING A MAIN BODY PORTION WITH AN OUTER WALL CONFIGURATION IN THE FORM OF A REGULAR POLYGON HAVING TWELVE OUTWARDLY EXTENDING POINTS OF A SIZE TO BE ENGAGED BY STANDARD SIZE WRENCH MEANS OF A SIZE LESS THAN USUAL FOR THE SIZE THREAD INVOLVED, THE CONTIGUOUS WALL SURFACES BETWEEN TWO SUCCESSIVE OUTWARDLY EXTENDING POINTS BEING AT LEAST IN PART SUBSTANTIALLY FLAT AND LYING IN PLANES INTERSECTING AT AN ANGLE OF ABOUT 130 DEGREES TO 138 DEGREES, THE WALL OF THE NUT AT THE INTERSECTION OF SUCH CONTIGUOUS WALL SURFACES HAVING A POSITIVE BUT MINIMUM RADIAL DIMENSION THROUGHOUT THE AXIAL EXTENT OF THE INTERSECTION OF THE WALL SURFACES, AS MEASURED TO THE BASE OF SAID THREADS, NOT GREATER THAN THE RADIAL DISTANCE BETWEEN THE BASE OF SAID THREADS AND A CONCENTRIC CIRCUMSCRIBING CIRCLE EQUAL IN RADIUS TO A CIRCLE INSCRIBED IN A REGULAR HEXAGON HAVING THE SAME MAJOR DIAGONAL DIMENSION ACROSS POINTS AS THE SAID REGULAR POLYGON WITH TWELVE POINTS. 